Continuous process for converting saponifiable fats into soap and glycerin



May 23, 1939. v, MlLLs 2,159,397

CONTINUOUS PROCESS FOR CONVERTING SAPONIFIABLE FATS INTO SOAP ANDGLYGERIN Filed Feb. 18, 1936 2 Sheets-Sheet l U a 5 E a E. n I; ,23 R

03 M s N Q m 1 K E i c 2- 1:: I a 21mm N v- N 1" N N [WATER Han-rs:

INVENTOR. V/ C TOR M IL 1. 5.

BY M I M ATTORNEYS.

WATER May 23, 1939. v. MILLS 2,159,397

CCNTINUOUS PROCESS FOR CONVERTING SAPONIFIABLE FATS INTO SOAP ANDGLYGERIN Filed Feb. 18, 1936 2 Sheets-Sheet 2 30A P POWDE R Cool. AIR

INVENTOR. V/c rare Mu. us.

By Mm fl ATTORNEYS,

Patented May 23, 1939 UNITED STATES CONTINUOUS PROCESS FOR (XJNVEBTINGSAPONIFIABLE FATS GLYCEBIN INTO SOAP AND Victor Mills, Cincinnati, Ohio,alsignor to The Procter & Gamble Company, Cincinnati, Ohio,

a corporation oi Ohio Application February 18, 1938. Serial No. 84,525

2 Claims.

My invention relates to a continuous process for converting saponifiabletats into solid comminuted soap and glycerin.

The objects of my invention are to provide a 5. continuous process forthe manufacture of comminuted soap and glycerin, including especiallythe production of a new form of comminuted soap having especiallydesirable properties, with a great saving in time and space over thathitherto required for accomplishing the same purposes, and a saving incost of operation.

This application is a continuation-in-part of my co-pending applicationSerial Number 21,845, entitled Continuous countercurrent hydrolysis offat.

Soap in comminuted form is becoming increasingly important to the soapmaker as its advantages are realized more and more by .the consumers. Itdisplaces soap in form of bars and flakes, not only for householdlaundry use but also for washstand toilet use in dispensers. The formsnow marketed range from finely divided, dry, dense particles, slow indissolving, such as shaving powders, to relatively large sized hollowparticles of very light weight, but quick to dissolve. A

product that is moderately dense, of rapid dissolving properties, andwith moderately high moisture content would have the most desirablecombination of properties, and this is accomplished in the presentinvention, which provides a new and continuous process for making same.

Heretofore the production of any form of comminuted soap has beencarried out in a series of separate operations, each of which involves aconsiderable amount of time and space and a loss of heat due to coolingbetween operations.

For example, the first step in the usual procedure has been first toconvert the fat, (meaning any saponiflable fat or fatty oil), into soapby the usual kettle boiling process which in most large soap factoriesconsumes a period of about ten days for the complete cycle of makingfinished soap in proper condition for further processing. The glycerinis recovered in this process in the form of a dilute solution containingusually from about five to fifteen per cent of glycerin and considerablesalt.

As an alternative procedure in the first step, soap has also been madefrom thefatty acids derived from saponiflable fats by hydrolysis, eitherin autoclaves at high temperature and pressure, or by the well knownTwitchell process. The fatty acids are saponifledwith a saponifyingagent such as a solution of caustic soda or of soda ash, and

converted into the same form of finished soap, all

of which procedure likewise consumes ordinarily several days. Glycerinsolution is obtained as one of the products of hydrolysis containingabout the same percentage of glycerin as in the aforementioned kettleprocess of making soap, but substantially free from salts.

In the next step the soap thus made by either procedure may be mixedwith suitable builders, etc., if desired, then heated to a suitabletemperature for spraying, and sprayed into a chamber where it comes incontact with heated, drying, or cooling air, or other gas, resulting inconversion of the molten soap into various comminuted forms withstructure, density, and moisture content varying greatly with thetemperature of the soap when sprayed and the temperature and volume ofthe gas with'which it comes in contact in the spraying chamber.

Inasmuch as either of these series of operations consumes several days,large amounts of material must be kept in process at all times to ensureuninterrupted operation; that is, if the complete series of operationsrequires twelve working days, for example, then the total material inprocess in the various stages would have to be substantially twelvetimes the amount of finished product required per day, thus requiring agreat deal of space and equipmeht for a given amount of dailyproduction. The materials at each stage of the processing naturally cooloff, and heat must be applied to reheat the material for the nextoperation.

My process offers a great improvement over these conditions in that itoperates continuously;

no reheating is required between operations, thussaving the loss andexpenditure for fuel and time; and the amount of equipment and spacerequired is extremely small for a given amount of product. The totaltime consumed in converting saponiflable fat into comminuted soap readyfor packaging by my process need not greatly exceed two hours, so thetotal material in process at any one time would be only that equivalentto two hours production.

My process consists briefly in first splitting the fat in a continuousautoclave process as described in my co-pending application SerialNumber 21,854, then passing the hot fatty acids issuing from same to amixer where they meet a continuous stream of saponifying agent suppliedin proper proportions, such as caustic soda solution for example,whereby saponification occurs almost instantaneously, and then themixture in the form of fluid soap containing a properly controlledamount or moisture passes without interruptiontoanosslewhereitissprayedintoasuitable chamber with a proper supply ofair or other cooling or drying ga's, resulting in the formation of solidcomminuted soap of unique structure and properties, in salable form,with practically any desired moisture content. Any desired builder suchas silicate of soda, soda ash. trisodium phosphate, borax, etc., may beadded to the solution of saponifying agent before mixing with the fattyacids, or added separately in the mixer, and thus produce a comminutedsoap containing such builder. Excessive amounts of crystalline builders,such as soda ash for example, are objectionable because they tend tomake a product having a definitely crystalline structure which producttends to break down in handling. I keep the proportion of crystallinebuilders, when used, below that which produces the above mentionedeflects. Hence my mixture as sprayed is a substantially homogeneousfluid mass of soap and water. with or without a builder, and forms asolid product that is also homogeneous, free from noticeable crystallinestructure, and resistant to breaking down with ordinary handling.

An important point in making products of good quality by my process isto protect the fatty material and the soap from contact with air orother oxidizing agents from the start until the product is cooled, inorder to avoid any darkening eflect due to oxidation.

Referring to the accompanying drawings:

Figure 1 shows a diagrammatic elevation view of an apparatus suitablefor carrying out the hydrolysis of the fat with resulting formation offatty acids and glycerin solution, and

Figure 2 represents a diagrammatic elevation view of an apparatussuitable for carrying out my whole process of converting fat intocomminuted soap.

40 Referring to Figure 1, l and 2 are deaerators or deoxygenators of anysuitable type for the water and fat respectively. 3 and l are meters formeasuring the two fluids. I and 0 are pumps for forcing the water andfat through the apparatus at the desired pressure. I and l are heatersfor water and fat respectively. 0 is a boiler or other device forsupplying heating means to the heaters l and 0. I0 is a tank for supplyof catalyst, in which is an agitator I I. I2 is a pump for deliveringthe catalyst into the fat. This pump preferably is so arranged as to actproportionally to the fat pump 0. i3 is a vertical autoclave chamberinto which the fat is fed at a point near the bottom throughdistributing pipes II and water is fed into the top through distributingpipes indicated by l5. I9 is a tank for receiving the "sweet water",into which it is flashed to atmospheric pressure. The concentrated sweetwater then is discharged through pipe 20, and the water vapor throughpipe 2|. 22 is a valve for suitably regulating the rate of discharge ofthe "sweet water", and 23 is an automatic pressure control valve on thefatty acid discharge. 2 and 25 are thermometers, respectively in thewater and fat inlet pipes to the autoclave i3. 28 is a liquid level gageto show the level of the interface between fat and water in theautoclave. The different parts of the apparatus are suitably connectedby pipes as shown and provided with additional valves where needed toproperly regulate the flow of the fluids. The autoclave i3 and otherparts of the apparatus coming in contact with split fatty acids shouldpreferably be made of a material resistant to the corrosive action offatty acids. The autoclave as shown and described herein is about twofeet six inches in diameter and flfty feet high, and well insulatedexternally to reduce losses of heat by radiation. It should be notedthat there is a space at the bottom of the autoclave, below fatdistributing pipes H, which will permit the sweet water" to settle andfree itself from globules of fat. The remainder of the autoclavecontains fatty matter through which the water is constantly passing. Atthe top of the chamber or autoclave above the water distributing pipesII, is a similar space to permit the fatty acids to separate completelyfrom globules of water before leaving the apparatus.

An exemplary operation of my process consists of the following. Instarting up, the water is first passed through the deoxygenator I,through the meter 8, pump I where the pressure is raised to any desiredpoint between 150 and 1800 pounds per square inch, sumcient to maintainthe heated water in the liquid phase at the temperature to which it isto be heated, while the pressure in the system is maintained by means ofvalve 22 (temporarily closed), and automatic pressure control valve 23,on the discharge from the autoclave ii.

The water next passes through the heater 1 where it is heated to thedesired temperature, between about 365 F. and about 800 F., and thenpasses into the autoclave II through the distributing pipe I! until theautoclave is filled with water. The supply of water then ceasestemporarily, and pumping of fat begins. The fat such as tallow in amolten state passes through the deoxygenator 2, meter 4, and pump 8where its pressure is raised to substantially the same point as that ofthe water. The fat then passes through the heater I where itstemperature is raised to about that of the water, and then it passesinto the autoclave through distributing pipes I 4. Any desired amount ofcatalyst, such as the oxide or soap of zinc, calcium, or magnesium, isintroduced into the fat by pump i2, preferably as the fat passes fromthe heater to the autoclave. The pumping of fat is continued withoutfurther addition of water until the autoclave is filled with fat abovethe level of the water distributing pipes H, which can be determined bythe use of a suitable liquid level gage 26, on autoclave II. The waterdispelled during this period of introducing the fat is allowed to escapethrough the control valve 22 at the water outlet at the bottom ofautoclave It, at the same rate as that of the fat introduced, whilemaintaining the desired pressure inside the autoclave to prevent thesuperheated water from boiling. The apparatus is now in condition forcontinuous operation.

Both fat and water are now supplied to the autoclave continuously at asteady rate. By supplying tallow at a uniform rate of about 500 poundsper hour in an apparatus of this size, and water at a rate of about 3500pounds per hour, while maintaining a temperature of about 470 F. and apressure of 600 pounds per square inch in the autoclave, the fat takesabout one hour to pass through the autoclave, and is hydrolyzed to theextent of over 98 per cent, and usually about 99 per cent. The splitfatty acids issue from the top of the autoclave through a. suitablepressure controlling valve in a continuous stream. A more rapid passageof the fat and water through the described apparatus in the samerelative proportions, taking for example 30 minutes instead of 60minutes, would still give a high degree of hydrolysis, only a few percent under that obtained grease? in 60 minutes. The liberated glycerinis taken up by the water and leaves the bottom of the autoclave in acontinuous stream in the form of a solution or "sweet water" which willcontain approximately 24 per cent glycerin, if the original fat was ofgood grade, containing substantially its full complement of glycerin. Inorder to provide a rather prolonged contact of water with fat, the mainbody of the autoclave should preferably be kept filled with fat throughwhich the water descends, and the interface between the fat and theaccumulated "sweet water should preferably be maintained in theapparatus described at a point about three feet above the bottom of theautoclave, or at about the level of the fat inlet it. This level can beregulated by suitably controlling the flow of the fat and the water, andcan be determined by use of suitable draw-oft valves at various levelsor by a liquid level gage.

The sweet water passes to the flash tank I! where its pressure isreleased through a suitable valve to atmospheric pressure, whereby aportion of the water suddenly evaporates to steam with a resultingcooling effect so that the temperature drops to slightly more than 212F. with a resulting concentration of the "sweet water" from a glycerincontent of 24 per cent to approximately 32 per cent. The split fattyacids issuing from the top of the autoclave may, if desired, be passedto a flash chamber maintained at any desired lower pressure, where thepressure is reduced if desired through a suitable valve, but I prefer topass the fatty acids without reduction of temperature or pressuredirectly to the mixer, as described below. The fatty acids while underthe temperature and pressure stated, if derived from fats of the tallowclass, contain approximately 11 per cent of water in solution, which,however, will partially flash into steam if the pressure is reduced,with a resulting cooling eifect on the fatty acids, but ordinarily thisentire moisture content is retained in the fatty acids as used in mypreferred procedure.

Both the fatty acids and the dissolved water in same are substantiallyfree from glycerin when the operation is carried out as described in anautoclave column of suillcient height. Thus, in a column ten feet high,I find that the water which is dissolved in the issuing fatty acidscontains about five per cent of glycerin; in a twenty foot column thewater contains only about one per cent glycerin, while in a fifty footcolumn as described herein the water contains only about 0.1 per centglycerin.

The fatty acids issuing from the autoclave I3 (containing dissolvedwater in amount depending on the temperature and pressure), and having atemperature above 212 F., preferably about 470 F., are then passed tomixer 30 through meter 29, while at the same time a solution of asaponifying agent, preferably caustic soda or soda ash in amount toproperly saponify the fatty acids, continuously controlled by a suitableproportioning device, is likewise passed continuously into the samemixer by pump 3i from tank 21 through meter 28. Meters 28 and 29 enablethe operator to control the flow of saponifying agent and fat in properproportions as des red. or they may be suitably connected with pump iiin an automatic proportioning device. When a built soap product isdesired, the solution of builder may be added to the solution ofsaponifying agent, or it may be added to the mixer separately inproperly and continuously proportioned quantities. The total amount oiwater introduced in the mixer is so regulated as to give the -isnecessary in the mixer or subsequently, be-

cause the fatty acids as received from the autoclave system alreadycontain an adequate amount of heat for the subsequent operations, havinga temperature preferably in the neighborhood of 470 F. The saponifyingagent does not need to be heated more than enough to have it in goodpumping condition but it may be heated, if desired, to impart additionalheat to the soap before spraying to secure maximum evaporation. Themixer must necessarily be kept under a suillcient pressure to preventvolatilization of the water at the temperature of mixing, and should beof sufllcient size and capacity to keep the materials in contact witheach other long enough to insure intimate contact and completion of thechemical reaction. This period need not ordinarily exceed one minutewith an efficient mixer.

The hot soap mixture then passes directly to the spray nozzle 82 andissues therefrom into the spray chamber 33 in comminuted form. Inasmuchas the soap mixture reaches the nozzle at a temperature considerablyabove 212 I".,

usually about 250-400 F., and under superatmospheric pressure, thepressure drops suddenly to that of the spray chamber, usuallyatmospheric pressure, with a consequent drop in temperature andinstantaneous evaporation of a portion of the water content in the soap.In making my preferred form of product, cooling air is admitted at thebottom of the spray chamber through openings 34 in order to cool theproduct sufllciently to keep the particles from sticking together, andpasses outward at the top through exhauster 35, thus incidentallycarrying away the water vapor volatilired from'the soap mixture. Thesoap mostly falls to the bottom of the chamber where it can becontinuously removed through air lock 36 for packaging, or for furtherprocessing into other forms if desired. Any fine material which may passout of the top of the chamber with the air is caught in a suitable dustcollector.

Other types of spray dried soap may of course be produced if desired,such as the well known Lamont product described in U. S. Patent1,652,900, by suitable modifications of the procedure in the spraydrying chamber.

The air supplied to the spray chamber may be introduced in either aconcurrent or countercurrent direction with the flow of soap, and bysuitable adjustments of the temperature of air, temperature of. soap,and volume of air, practically any desired variation in moisturecontent, or size, of particles may be obtained.

The preferred soap product obtained as described is novel as far as Iknow in consisting of feather-like, irregular shaped solid, not hollow,particles of size easily visible to the naked eye, substantially freefrom glycerin, and may contain practically any desired amount of moisture, percentages between 15 and 25 being especially desirable andreadily obtainable, but ten per cent is approximately the lowestpercentage readily obtainable in practical operation. A

product with lower moisture constant may, however, be obtained by usingmolten caustic sodainstead of an aqueous solution of same forsaponifying. The particles mainly sink in water, but form a bulk producthaving a bulk density usually of about .25 to .40 as compared withwater, due to irregular structure of the individual particles whichprevents the particles from packing tightly together, very readilysoluble, and fairly free flowing, non-dusting, and shows little or notendency to lump or ball together in water. In these latter respects itcompares favorably with spray dried products of the rounded, puffed,thinwall type, such as those described in the patent to Lamont No.1,652,900, which are noted for their ready solubility and their freeflowing qualities, but which are light bulking and usually of lowmoisture content. My product as described dissolves in 10 to 15 secondsin the solubility test described in Lamonts Patent No. 1,652,900, asfollows:

These flgures on speed of solubility were determined by placing gm. ofsoap product in $5 liter of water at 110 F. and stirring the productwith a tablespoon at the rate of 25 double strokes per quarterminute.The container holding the soap and water was provided with an internalremovable screen which was lifted out of the water at desired intervals,say 10 to 15 seconds, and if any soap remained undissolved it could beseen on the screen."

I attribute the rapid solubility of the particles of my preferredproduct, in spite of their solid interior, to the fact that theparticles are thin, have a large irregular surface due to the burstingor explosive effect in their formation, and to the fact that they havenot acquired a hard dried skin on the surface of the particles, such aswould result from exposure to a highly heated drying gas. All the heatfor drying my product is stored up within the product under hightemperature and pressure conditions before reaching the spray nozzle,and on issuing from the nozzle at a lower pressure there results abursting or disintegration of the particle due to the instantaneousvolatilization of moisture contained in same.

The glycerin solution continuously discharged from the autoclave in myprocess has a concentration of approximately fifteen to forty per cent,usually about twenty-four per cent under the preferred conditionsdescribed, and is substantially free from salts. This may be furtherconcentrated by flashing" or suddenly subjecting it to a lowertemperature and pressure, in which case the concentration may be raisedfrom twenty-four per cent to as high as thirty-two per cent glycerin.This is much higher than is obtainable in the commercial operation ofother soap making and glycerin recovery processes. This solution is thensubjected to the ordinary purification, evaporation, and distillationproccases to obtain the pure glycerin of commerce. The recovery cost isobviously much lower than in prior known processes because of the higherinitial concentration of the glycerin solution and absence of dissolvedsalts.

The oomminuted soap thus obtained in thisprocesscannotonlybeusedandsoldassuch, but it may also be readilyconverted into other forms of soap-products such as flakes, bars, orextruded forms. For this purpose it is only necessary to produce flrstthe comminuted soap having' the formula and moisture content desired,and then pass it through rolls to convert it into flakes, or throughsuitable rolls and plodders or other known equipment to convert theparticles into the form of extruded bars.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. That method of preparation of soap, which consists in continuouslyforming fatty acids from fats at high temperature and pressure byhydrolysis using an excess of water over that required for hydrolysisand by control of temperature during hydrolysis controlling the waterdissolved in the resulting fatty acid to a definite percentage, thenwithout substantial reduction of temperature and pressure or exposure ofthe fatty acids to oxidation combining said fatty acids with alkalisolutions in combining proportions and containing a definite percentageof water the total combined water being not more than will form a neatsoap, said fatty acids and alkali being maintained in a state of flow,and finally discharging the resulting soap at a temperature between 250to 400 degrees F. into a zone of lower temperature and pressure.

2. That process for continuously producing soap from fats suitable forsoap making and alkaline reagents for the saponiflcation thereof whichconsists in first causing the fat to flow countercurrent to water in asuitable vertical chamber at a high temperature under sufllcientpressure to maintain the water in a liquid condition, the period ofcontact of fat with water being sufli cient to cause a substantialsplitting of glycerin from the fatty acids, second continuously removingthe fatty acids with the water dissolved in same and the sweet waterresulting from said treatment in separate streams, third continuouslycommingling in an enclosed space under pressure the fatty acids withoutsubstantial reduction of temperature with an alkaline reagent and water,the said water thus added together with the water dissolved in the fattyacids being substantially no more than enough to result in the formationof neat soap, and the said alkaline substance being in substantiallycombining proportions, and fourth delivering the resulting soap at atemperature between 250 and 400 degrees F. to a point for cooling thesame.

VICTOR MIILS.

